Frequency-changer.



No. 869,413. PATENTED OCT. 29, 1907.

W. S. BRALLEY.

. FREQUENCY CHANGER.

APPLICATION IILED FEELS, 1907.

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No. 869,413. PATENTED OCT. 29. 1907. W. S. BRALLEY. FREQUENCY CHANGER.

APPLICATION TILED FEB. 5, 1907.

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ATT'Y UNITED STATES PATENT OFFIC WAL TER S. BRALLEY, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF "NEW YORK.

FRE QUEHCY-CHANGER.

Specification of Letters Patent.

Patented Oct 29', 19v 4 Apnlicstiou and February 5. 1907." shin No. assess.

object is to provides. novel means for tying together a two transmission systems of different frequency, so as to enable one' system to supply power to the other.

It occasionally ha ensthat own-transmission s s,'

t PP P terns of different frcquencymay be extended into proximity to each other, and that it is desired to tie the two s3 stems together, so that one system may hclpout'the.

other at times-of overload. For this purpose frequency changers have been employed heretofore, consisting of synchronous motor-generator sets. Such a set is not wholly satisfactory for this purpose, since in the first place the load on the set is determined by the relative field-strength oi the machines and cannot readily be controlled automatically; and in the second place if a short-circuit occurs on one system, the set is overloaded and may he thrown out of step giving a short-circuit on the second system before the circuit hreakersopen.

My in ention consists in employiiig in place of the synchronous motor-generstorset a pair of asynchronous induction machines with short-circuited secondaries, primaries supplied from the two systems, respectively,

the load on the machine I rely on the fall in frequency of the overloaded system. This drop, if the speed-governors itll the generating station are not adjusted for close regulation, will be sufficient to load the frequency generator, for if us two machines are designed to rotate at the me speed when both systems are lightly loaded, then when the frequency of one system falls, the speed of the induction machine connected to that system tends to fal so that it acts as an induction generator driven by e other machineas a' motor. Since, in large machines, the full-load slip may be less than one per cent, a drop in frequency of less than two po -"cent. in one of the systems will result in a transfer at power from one system to the other equal in amount to the full load of the "es. The control'of the load on the set is thus entire y automatic. Furthermore; a. short-circuit on either system can have no bad effect upon the set, since the magnetizing current of the machine connected to the short-circuited system'imrnedistely fails and the other machine runs idle under the frictional load of the set. i

My invention further comprises an overload device arranged to insert resistance in the circuit of one of the -machines. 'For the operation of this device I utilize :the increase in slip due to an overload, by employing a smell induction machine with its rotor on the same shaft with the main machines, and a stator rotatably mounted but restrained from movement by a spring. Thishninll' regulating machine may be supplied from either transmission system. With ordinary slips its torque is small, hut with an abnormal increase of slip 1 its torgueingreasesfso as'to produce a movement of the stator which-"hwy be utilized to actuate h resistancecontrollirfg My inventionl will best be understood by reference to the accompanying drawings,-in which Figure. 1 shows -a sideelevationof a frequencychanger arranged in accordance with my invention;

Fig. 2 shows an enlsrgedviewfportly in cross-section, of the induction governor; Fig. 3 shows an endelevution of the same; end-Fig. t shows diagrmnmstically the connections and iirrang ement of windings of the machines -In the drawings A and B represent the stators of two, induction machines, of which the rotors are-m0unted on the same shaft. These nuichines are arranged with different numbers of poles corresponding to the m quencies of the systems to which their primaries are connected. For instance, if the frequencies of the two system's ai re 40 and 25 cycles, the stator A may be or ranged Ior 10' poles and the stator Him 16 poles. and rotors mechanically connected. For controlling 1 the'ststor of which iiieprigizted by D This stator is rotatahly mounted, shown in. F restrained from movement hy'sprinke primary winding is co'nn ecfled in the main mines snd h'as poles. A dash-pot F e movement: of the stator D when it is moved' ia st th 'eltension of the springs'E. The stator co nectod mechanicslly in any suitable manner, as. G andpinion g, with a controlling switcli hich controls the circuit of a. plurality of magneticslly aetuated switches or con factors "I, which, in turn, control resistances J connected to the secondary I; through the collector-rings b. The stator D is normally held in the position shown in the drawings so that switch H is normally in the offposition, all of magnet windings L are denergized, and resistances J short-circuited. The small induction machine is an overload device, and in normal operation the resistances remain shortcircuited.

The operation of the frequency-changer is as follows: When both systems are unloaded, the speed at which the two induction machines tend to run is the same, so that they divide the friction load of the set. Now, if the frequency of one of the systems falls, due to a load on the 'systein, the speed at which the machine connected to that system tends to run is lowered, and if the speed is lowered a suificient amount, this machine tends to run as a generator driven by the other machine as a motor. Since the drop in frequency on the loaded system is proportional to the load, the difference in the speeds at which the two induction niachines tend to run is proportional to the load, and this difference determines the load on the machines, so that the regulation is'entirely automatic. If one system should be so heavily overloaded as to drop the frequency of the system below normal limits, thereby overloading the induction machines, the small induction machine D comes into action. Since the rotor of this machine is on the same shaft with the rotors of the main machines, its slip is the same as the slip of the main machines, and it is so designed that with normal slip, the torque between stator and rotor is not sufiicient to move the stator against the tension of springs E; but if the main induction machines are overloaded, so that the slip increases above normal value, the torque of the small induction machine is increased so that its stator is moved in onedirection or the other, according as its slip is positive or negative, so as to move switch H from its central position anC energize a portion or all of magnet windings I. These magnet windings act to insert portions of resistances J in circuit with the secondary winding b, thereby decreasing the torque between secondary b and primary B, in-

' creasing the slip and consequently reducing the load I do not desire to limit myself to the particular construction and arrangement of parts here shown, but aim in the appended claims to cover all modifications which are within the scope of my invention. 7

What I claim as new and desire to secure 'by Letters Patent of the United States, is,

1. In combination with two transmission systems, two asynchronous. induction machines having their ,primnrles supplied from said systems respectively, their secondaries shortcircuited, and their rotors mechanically connected to each other.

2. In combination with two transmission systems, two asynchronous induction machines having their rotors on. the same shaft and their primaries supplied from said systems respectively and their secondaries short-circuited.

3. In combination with two transmission systems, two asynchronous induction machines having their primaries supplied from said systems respectively, their secondaries short-cireuited, and their rotors mechanicaliyconnected to each other, and means for automatically controlling the' slip of said machines on overload.

4. In combination with two transmission systems, two asynchronous induction machines having their primaries supplied from said systems respectively, their secondaries short-circulted, and their rotors mechanically connected to each other, and automatic means for increasing the resistance of the secondary circuit 01! one 0! said machines upon an overload. 4

5. In combination with two trnnsmission'systems, two asynchronous induction machines having their primaries supplied from said systems respectively, their secondaries B0 short-circuited, and their rotors mechanically connected to each other, a small induction'machine supplied from one of said systems having its rotor mechanically connected to the rotors of the main machines and its stator rotntablymounted, yielding means tor restraining the movement of the stator, .and means controlled by .the movement of said stator for. varying the resistance ottho secondary circuit of one of the main machines. 7 6. In combination with two transmission systems, .two asynchronous induction machines having their primaries supplied from said systems respectively, thcir econdaries sliort-circuited, and their rotors mechanically connected to each other, a small induction machine supplied from one" 01 said systems having its rotor mechanically connected to the rotors of the main machines and its stator rotatably mounted, a spring opposing the movement oi! the stator, a switch mechanically connected to the stator, and a resistance controlled by said switch in circuitwith the, secondary winding-of one of the main machines. 7. In combination with two transmission syltems, two asynchronous machines having their primaries supplied I from said systems respectively, their secondaries shortcircuited, and their rotors mechanically connected to each other, an overload device, and means controlled thereby for inserting resistance in the secondary circuit of one 105 of said machines.

In witness whereof, I have hereunto set my hand and affixed my seal this 2nd day of February, 1907.

WALTER S. BRALLEY.

Witnesses BENJAMIN B. HULL, HELEN Onrono. 

